sorry for the late reply, had to work a little late.
yes, shifter should be in park, and as for the pack, it will only line up with the shifter assembly and engage it one way only.
that detent latch should only line up one way. and line straight up with the shifter tab.
Im not a big you tube fan, but there is a video of a guy replacing a 45rfe sol pack, and its a pretty decent video.
I have included the link for you here
once you line it up, it should only go one way to lock in to that shift tab.
good luck with your repair!
thanks and i appreciate positive ratings